Vehicle fuel delivery systems may include a direct fuel injector to inject fuel directly into a cylinder of an engine. The direct fuel injector may deliver fuel in proportion to a fuel injector pulse width of a signal from an engine controller. However, due to aging, fuel contamination, or hardware failure, the fuel injector may degrade and deliver undesired additional fuel. When more fuel is delivered to the engine than intended, the engine may run rich and experience an air-fuel ratio (AFR) imbalance between cylinders. An AFR imbalance between cylinders occurs when the AFR in one or more cylinders is different than the other cylinders. Control strategies may be able to correct for the undesired additional fuel by decreasing fueling, for example, using feedback from an exhaust gas oxygen sensor. However, if the amount of undesired additional fuel is considerable, the cylinder receiving fuel from the degraded injector may misfire. Consequently, a non-combusted air-fuel mixture may be displaced into exhaust gas. The non-combusted air-fuel mixture in the exhaust gas may participate in an exothermic reaction at an exhaust treatment catalyst, generating heat that may degrade the catalyst and other exhaust components. Therefore, it is advantageous to quickly identify a degraded fuel injector delivering undesired additional fuel so that mitigating actions may be performed.
Various strategies exist for identifying a degraded fuel injector, for example, by monitoring a change in fuel rail pressure (e.g., by utilizing a pressure sensor) at a start of an injection event or during non-fueling conditions. One example approach is shown by McEwan et al. in U.S. 20160245221 A1. Therein, identifying a degraded fuel injector includes monitoring a change in fuel rail pressure over a period of time during non-fueling conditions, when fuel is shut off to all cylinders. If undesired fuel delivery is absent, then the change in fuel rail pressure may be less than a threshold change. However, if undesired fuel delivery is present, then the change in fuel rail pressure may be greater than or equal to the threshold change.
However, the inventor herein has recognized potential issues with such systems. As one example, although the above method identifies that a degraded fuel injector is present, it may be time consuming to determine which fuel injector is degraded, resulting in lengthy diagnostic and repair procedures. Further, the inventor herein has recognized that variable displacement engine (VDE) technology may be utilized to pinpoint a degraded injector. Variable displacement engines are configured to operate with a variable number of active or deactivated cylinders to increase fuel economy. For example, a portion of the cylinders may be deactivated during selected conditions, wherein the selected conditions are defined by parameters such as an engine speed/load window and vehicle speed. A VDE control system may disable selected cylinders through the control of a plurality of cylinder valve deactivators and by deactivating fuel injectors that fuel the selected cylinders. Thereby, the deactivated cylinders are not fueled, and intake and exhaust valves of the deactivated cylinders are closed. Further, spark is disabled to the deactivated cylinders. However, liquid fuel may accumulate within a deactivated cylinder if the deactivated cylinder has a degraded fuel injector.
Thus, in one example, the issues described above may be addressed by a method comprising, responsive to an indication of an air-fuel combustion gas imbalance from cylinders of an internal combustion engine, deactivating a subset of the cylinders, including deactivating fuel injectors delivering fuel to the cylinder subset; and inferring a first output of each of the cylinders during the deactivation after a duration of deactivation has elapsed. In another example, the method further includes reactivating the subset of cylinders for a duration to expel any liquid fuel; deactivating the subset of cylinders; and inferring a second output of each of the cylinders during the deactivation. In this way, a cylinder with a degraded fuel injector may be conclusively identified responsive to the first output of the cylinder being less than a threshold and the second output of the cylinder being greater than the threshold.
As one example, all of the cylinders of a first engine bank may be deactivated responsive to the air-fuel combustion gas imbalance indicating that the first engine bank is rich relative to a second engine bank. However, hardware limitations may restrict which cylinders may be deactivated and thus, in another example, a subset of cylinders from each engine bank may be deactivated. Therefore, the exact cylinder with the degraded fuel injector may not be conclusively identified, but may be narrowed down from all possible cylinders.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.